Abstract: A new contact algorithm for sliding surface based on triangular subdivision local search has been developed for the clear description of complex contact-impact interface in the Lagrangian numerical simulation of weapon dynamics. In this algorithm, a four-node quadrilateral contact surface segment is subdivided into four triangular sub-segments in which normal vectors are confirmed by a shape heart introduced by averaging the positions of the four contact segment nodes. The contact status and the contact point of a node respected to the surface are judged according to the relative position of this node and the sub-segments. Then the interface is described by performing the contact constraints on the nodes of the interface. This algorithm can resolve the problems of conventional contact algorithms such as iterations and the deadzone problems, and can conquer the difficulty of contact point determination when the mesh is severely distorted. Numerical results show that the new contact algorithm is cost effective and robust.